Didn't Meeks go from being our DC back to our Secondary coach?
Demotions of assistants happen, but even those are rare. Demotions of head coaches? Pretty much never.
Besides the fact that most guys would be too proud to accept it, doing so saddles a new coach with an existing DC that he may not want. New HCs tend to want to choose their own staff.
As to the question, if the Panthers have a top 5 defense but a losing record, I'd say the current staff stays intact at least at the top. Rivera may want to make a few changes in the assistant ranks.